1. Field of the Invention
The present invention relates to a thermal liquid ejection head used in an ink-jet printer head or the like, and also to a liquid ejection apparatus such as an ink-jet printer using a liquid ejection head. More specifically, the present invention relates to a technique to realize a structure for supplying liquid with minimized ejection variations.
2. Description of the Related Art
One known liquid ejection head for use in a liquid ejection apparatus such as an ink-jet printer is a thermal liquid ejection head which operates using expansion and contraction of a generated bubble.
In this thermal liquid ejection head, heating elements are disposed on a semiconductor substrate, and bubbles are generated in liquid chambers by heating elements, thereby ejecting liquid droplets from nozzles disposed on the respective heating elements toward a recording medium.
FIG. 12 is a perspective view showing the appearance of a liquid ejection head 1 of the above-described type (hereinafter, referred to simply as the head 1). In FIG. 12, the nozzle sheet 17 formed on the barrier layer 3 is shown in the form of an exploded view.
FIG. 13 is a cross-sectional view showing the flow channel structure of the head 1 shown in FIG. 12. The flow channel structure of the liquid ejection apparatus of this type is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2003-136737.
As shown in FIGS. 12 and 13, a plurality of heating elements 12 are disposed on a semiconductor substrate 11. A barrier layer 3 is formed on the semiconductor substrate 11, and a nozzle sheet (nozzle layer) 17 is further formed thereon. Each part including a heating element 12 and a part of the barrier layer 3 formed on the semiconductor substrate 11 is referred to as a head chip 1a. A part including a head chip 1a and a nozzle 18 (nozzle sheet 17) is referred to as a head 1.
In the nozzle sheet 17, nozzles (holes via which to eject liquid droplets) 18 are formed at locations corresponding to the respective heating elements 12. The barrier layer 3 is formed on the semiconductor substrate 11 and between the heating element 12s and the nozzles 18s such that a liquid chamber 3a is formed between each heating element 12 and a corresponding nozzle 18.
As shown in FIG. 12, the barrier layer 3 is formed so as to have comb-like fingers, and each heating element 12 is disposed between two adjacent fingers such that three sides of each heating element 12 is surrounded by the barrier layer 3 when seen in horizontal cross section whereby each liquid chamber 3a is formed such that only one side is open. Each opening forms an individual flow channel 3d communicating with a common flow channel 23.
Each heating element 12 is disposed on the semiconductor substrate 11, at a location close to one side of the semiconductor substrate 11. As shown in FIG. 13, a dummy chip D is disposed on a left-hand side of the semiconductor substrate 11 (head chip 1a) such that a common flow channel 23 is formed between one side face of the semiconductor substrate 11 (head chip 1a) and one side face of the dummy chips D. Note that the member disposed on the left-hand side of the semiconductor substrate 11 is not limited to the dummy chip D, but another member may be used as long as the common flow channel 23 can be formed.
On the semiconductor substrate 11, as shown in FIG. 13, a flow channel plate 22 is disposed on a surface opposite to the surface on which the heating elements 12 are disposed. In this flow channel plate 22, as shown in FIG. 13, an ink supply inlet 22a and an ink supply flow channel (common flow channel) 24 are formed such that the ink supply flow channel 24 is substantially U shaped in cross section and such that the ink supply inlet 22a communicates with the ink supply flow channel 24. The ink supply flow channel 24 and the common flow channel 23 communicate with each other.
In this structure, ink is supplied via the ink supply inlet 22a into the ink supply flow channel 24, then into the common flow channel 23, and finally into the liquid chamber 3a via the individual flow channel 3d. A bubble is generated on the heating element 12 in the liquid chamber 3a by heat generated by the heating element 12, and a flight force is generated when the bubble is generated whereby the liquid (ink) in the liquid chamber 3a is partially ejected in the form of a liquid droplet from the nozzle 18.
Note that in FIGS. 12 and 13, the shapes of respective parts are drawn in an easily understandable manner and the drawn shapes are not necessarily exactly similar to the actual shapes. For example, the thickness of the semiconductor substrate 11 is about 600 to 650 μm, and the thickness of the nozzle sheet 17 and that of the barrier layer 3 are about 10 to 20 μm.
A first method of producing the head 1 is to bond the head chip 1a produced using a semiconductor process to the nozzle sheet 17 produced separately. This method is called a chip mounting method. A second method is to produce nozzles (on-chip nozzles) 18 integrally on a semiconductor substrate 11.